Variation in state of charge (SOC) indicating a charged state of each of a plurality of battery modules that is coupled in series and that is used as a single storage battery could restrict charging of one of the battery modules, which has the maximum SOC, as well as could restrict discharging of another one of the battery modules, which has the minimum SOC.
As a cell balance controlling method for straightening SOCs in a plurality of battery modules coupled in series, PTL 1 describes, as a conventional art, a method through which resistors and switching elements are coupled in parallel so as to correspond to respective battery modules to cause one of the battery modules, which has a higher SOC, to discharge electricity by means of corresponding one of the resistors to straighten its SOC with SOCs in the other battery modules.
As a technique relating to the present invention, PTL 2 discloses, as a vehicular power supply device, a configuration including a first measuring circuit for detecting a voltage in a battery for travelling, a second measuring circuit for detecting overdischarging and overcharging, a high voltage power supply that uses electric power supplied from the battery for travelling, a low voltage power supply that uses electric power supplied from a battery for electric components, and an insulating circuit disposed between the respective first and second measuring circuits and electric components. Here, the high voltage power supply supplies electric power to the first and second measuring circuits, while the low voltage power supply supplies electric power to the insulating circuit.